The relationship between bone resorbing factors and loosening after hip prosthetic replacement.

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The progressive enlargement of the radiolucent area has often been observed around the implant, leading to loosening of the prosthesis. The purpose of this study is to elucidate the mechanism of rediolucent area formation. The radiolucent areas could be classified into the linear type and the erosive type, and these two groups were compared as to the histological and biochemical results. The interface membranes were obtained from patients at the time of surgery for revision of either cemented THA or cementless bipolar endprosthetic replacement.The bone resorption around the implant after hip prosthetic replacement occurs in two different pathways. The first pathway may be cnhanccd bone resorption by chemical mediators and enzyme derived from foreigne body granulomas. The second possible pathway would be the bone necrosis by mechanical stresses due to biomechanically unstable implant.Histologically, the interfaces of the osteolysis type contained more debris, macrophages, and giant cell … More s than the linear type. Some macrophages, giant cells and synovial like cells were positively stained with anti-interleukin-6 antibody and TRAP.The levels of IL-6 and IL-8 in the homogenates from osteolysis type were significantly higher than those from the lincar type. The interface membrancs were dissociated by collagenase, and cultured on dentine slices from 2 hours to 1 week in order to study whether the macrophages and giant cells can resorb bone by themselves. Most of coltured cells were stained with NSE of a marker of macrophage, and weren't stained with TRAP at 2 hours. TRAP positive mononucleated and polynucleated giant cells were increased at 1 week, but both of resorption pit and F-actin ring formation weren't observed.According to these findings, macrophages in osteolysis produce IL-6 which activated osteoclast in host bone, and IL-8 which might relate to the formation of foreign body granuloma in addition to the phagocyte of debris. Although some macrophages are stained with TRAP, it might be difficult for macrophages to differentiate to the osteoclast like cells which were capable of bone resorption. Less